The present invention relates to surgical operation devices for crushing, severing and/or cutting the organization of an organism using ultrasonic vibrations.
Known operation devices which use ultrasonic waves are devices for crushing and/or cutting the organization of an organism in the fields of orthopedic and general surgical operations, devices for operating cataract in the field of ophthalmology and ultrasonic operation devices for scaling the teeth in the field of dental surgery. Any of these devices includes an ultrasonic oscillator, an ultrasonic piezoelectric transducer, an ultrasonic wave transmitter which constitute a single resonant system which oscillates ultrasonically at a particular resonant frequency. Usually, the operation section of the ultrasonic vibration transmitter contacts an organism, so that a mechanical load acts on the operation section. The load on the oscillator fluctuates in accordance with contact state. Therefore, the oscillating frequency and mechanical resonant frequency of the oscillator differ from each other and it is difficult to maintain the amplitude and vibrating speed of the operation section at constant appropriate conditions.
In order to cope with such fluctuations of the load, an oscillation feedback oscillation is known in which if an ultrasonic vibration transmitter is connected and driven with a constant current or voltage, in order to cope with fluctuations of the load, the mechanical Q of the resonant system is high, so that the amplitude and vibrating speed of the operation section is maximum at the mechanical resonant frequency. This amplitude and vibrating speed are extracted by using an appropriate device or method proportional to the amplitude and fed back to the input terminal of an amplifier to maintain oscillation at all times even if the mechanical resonant frequency fluctuates. An oscillator is used in which a pickup device is attached to a piezoelectric transducer to obtain a voltage in proportion to vibration and to feed back the voltage to the input terminal of the amplifier. The attachment of the pickup device to the transducer renders structurally complicated and a large-sized handpiece including the transducer. This is against miniaturization and lightening of the handpiece as an operation device for medical treatment manipulated by the operator.
There is proposed a method in which a voltage in proportion to the vibration is extracted by an electrical circuit. In this case, an oscillator is used in which an oscillating voltage detector is used as a feedback circuit (see FIGS. 20, 21). A voltage in proportion to the vibration is extracted as an output voltage 105 to a transducer 104 from a matching circuit 102 by an oscillating voltage detecting motional bridge 107 of a feedback circuit 103 and fed back to the input terminal 106 of an amplifier 101, as shown in FIGS. 19 and 20. If a load is applied to the operation section before oscillation starts, the mechanical resonant frequency of the resonant system including the piezoelectric transducer and the ultrasonic vibration transmitter greatly tends to be a spurious frequency at the start-up. In addition, under such condition, the oscillation is fixed by the feedback circuit 103 in the spurious mode, so that it is difficult to restore the predetermined mechanical resonant frequency. If the difference between the mechanical resonant frequency and the oscillating frequency is out of the narrow resonant frequency of the matching circuit 102 of the oscillator or of filters of the amplifier 101 by fluctuations of the load on the vibrating operation section, feedback would not be effected and oscillation would stop undesirably.
An ultrasonic oscillator including a feedback circuit using a PLL (Phase-Locked Loop) (Japanese Patent Publication JP-A-61-10194) uses the feature of the PLL to cause a piezoelectric transducer to sweep frequencies in a predetermined range to lock the oscillating frequency to the mechanical resonant frequency. If the resonant system is driven which includes an ultrasonic vibration transmitter connected to the piezoelectric transducer and has a greatly changing load thereon, the direct supply of a feedback signal from the transducer to a phase comparator of the PLL makes it impossible to discriminate between the spurious frequency and the optimum resonant frequency generated when the amplitude and vibrating speed of the operation section are maximum and the vibration may be likely to be fixed in the spurious mode. Thus, especially, it is difficult to vibrate an ultrasonic vibration transmitter in large load fluctuation and especially used for severing and/or cutting a hard organization.
While a magnetostrictive transducer is often used as a power transducer, the efficiency of its electro-mechanical conversion is low, radiation loss from the transducer is high and the transducer would be deteriorated unless it is cooled by water, for example. Thus, a power electrostrictive bolted Langevin transducer higher in electro-mechanical conversion efficiency than the magnetostrictive transducer has been invented. The Langevin transducer is low in heat generation compared to the magnetostrictive transducer, so that a special-purpose cooling mechanism is not needed. FIG. 21 schematically illustrates a Langevin transducer in which one of metal blocks 108, 109 has a bolt portion and the other has a nut portion. The bolt portion has ring-like polarized electrostrictive transducers 112, 113 and electrodes 114, 115, 116 fitted alternately thereon and tightened by the other (nut) of the blocks 108 and 109. High-frequency power is applied across the electrode plates 114, 115 and 116 from the oscillator to cause ultrasonic vibrations. At this time, the metal block 108 contacting the ultrasonic vibration transmitter 117 which directly contacts the organization of an organism have to be used grounded. According to classification of dangerous degree of electrical shocks this system is a B-type medical device, so that it cannot be applied directly to human hearts.
One example of the structure of a conventional handpiece using an ultrasonic vibration transmitter to crush, suck and eliminate a soft organization will be described somewhat in detail with reference to FIG. 22. An ultrasonic vibration transmitter 119 is connected to an ultrasonic vibration source 118 as by screws. The transmitter 119 includes a constant cross-sectional area (for example, cylindrical) portion 126 of a 1/4 wavelength, a tapered portion and a minimum-diameter pipe-like operation section 122 for generation of ultrasonic vibrations. The transmitter 119 has a longitudinally extending internal path 120 through which celluar fragments crushed and emulsified by the operation section 122 and an irrigation solution supplied to a position where operation is effected are sucked and eliminated to the outside.
The distribution of stress on the transmitter 119 is expressed by a stress line 123 in FIG. 22(b). The internal stress produced when ultrasonic vibrations occur is zero at the end of the ultrasonic vibration source 118 and the operation section 122. The maximum point on the stress line 123 appears at the minimum cross section area 121 of the tapering portion. FIG. 22(c) illustrates the amplitude corresponding to the stress. The amplitude amplification rate is directly proportional to the ratio of cross section area S.sub.1 of the cylindrical portion 126 to cross section area S.sub.2 of the operation section 122, S.sub.1 /S.sub.2. Similarly, the internal stress is also proportional directly to the cross section area ratio between portion 126 and 121.
A large amplitude is required to crush the organization of an organism, especially, calcification so that it is necessary to increase the cross section area ratio in the ultrasonic vibration transmitter 119. As a result, a metal fatigue and hence breakage due to ultrasonic vibration may occur at the minimum tapering end 121 to which the maximum stress applies. Thus, if a high-amplitude handpiece is designed which prevents a breakage at the minimum cross section area 121, it would be greatly deformed and not suitable for practical use.
If a position where operation is effected is deep in a living body and the operating field is very narrow, very difficult operation is forced to thereby take a long time, which is an obstacle to an appropriate and accurate operation.
When a hard organization is conventionally severed and cut, Kerrison foceps, chisels, raspatories, surgical burs, etc., are used. Operation devices such as Kerrison foceps and line saws are low in operation efficiency, take much time, take much energy from the operator, and require fine operation and high techniques. An air-driven surgical bur rotates a drill to sever and cut the affected portion of a living body, so that small vibrations are transmitted to the hand of the operator from an area where the bur contacts the hard organization during operation, and hence a fine operation is difficult. In addition, the activeness of the organization of an organism would be lost by frictional heat due to rotation of the drill. Furthermore, the rotational movement of the drill would damage the organization of blood vessel and nerves in a hard organization only by touching the organization.